The conventional schemes proposed in IETF (Internet Engineering Task Force) (for example, Govind Krishnamurthi, Robert C. Chalmers, Charles E. Parkins, “Buffer management for smooth handovers in ipv6.,” INTERNET DRAFT, March 2001) involve handover control to buffer packet data.
In this handover control, packet data is buffered in an edge router provided in a base station during a handover of a radio terminal unit, in order to implement handover control without loss of packet data. After completion of the handover, the buffered packet data is forwarded to an edge router at a destination.
A configuration of a mobile communication system performing such handover control is presented in FIG. 6 and will be described below.
This mobile communication system shown in FIG. 6 is comprised of a radio terminal unit 10 which is a mobile communication means such as a cellular telephone or the like, a plurality of base stations 12, 14, 16 for radio communication with the radio terminal unit 10, edge routers 18, 20, 22 provided in these base stations 12-16, and CORs (Cross Over Routers) 24, 26, 28 connected to these edge routers 18-22. Here the CORs 24-28 are arranged in a hierarchical structure with COR 28 at the top, in which the edge routers 18, 20 are under COR 24, the edge router 22 under COR 26, and the edge routers 18-22 under COR 28 through CORs 24, 26.
In this configuration, the data buffering point was the previous edge router 20 in the handover control during movement of the radio terminal unit 10 from a covered area of the edge router 20 to a covered area of the edge router 22. In this handover control, all packet data transmitted from an unrepresented correspondent node as a sender during the handover of the radio terminal unit 10 was once forwarded through CORs 28, 24 to the previous edge router 20 connected before the movement, as indicated by an arrow Y1, and buffered therein.
After completion of the handover of the radio terminal unit 10 to the edge router 22, an instruction is then given to instruct the previous edge router 20 to forward the buffered packet data and in accordance with this instruction, as indicated by an arrow Y2, the packet data is forwarded from the edge router 20 through a plurality of CORs 24, 28, 26 to the radio terminal unit 10 connected to the new edge router 22 after the movement. The lossless handover was achieved by the buffering in the previous edge router 20 in this way.